Recently, capsule endoscopes have been increasingly used for making diagnoses of digestive organs in living bodies. Known prior art capsule endoscopes for these diagnoses are described in, for example, U.S. Pat. No. 6,939,295 and in International Patent Publication WO 02/054932A2.
FIG. 21 shows an exemplary structure of a prior art capsule endoscope described in U.S. Pat. No. 6,939,295, and FIG. 22 shows an exemplary structure of a prior art capsule endoscope described in International Patent Publication WO 02/054932A2. In the capsule endoscope having the structure shown in FIG. 21, an objective optical system 52 faces a dome-shaped transparent cover 51, an image pickup device 53 such as a CMOS is provided at the imaging position of the objective optical system 52, and light sources 54, 54 such as white LEDs, are provided around the objective optical system 52.
The image pickup device 53 is connected to a drive and processing circuit 55. The drive and processing circuit 55 includes a DSP (digital signal processor) circuit for converting analog signals from the image pickup device 53 to digital signals and a light modulation circuit for changing the brightness of the light sources 54, 54 according to image information. A circuit board that includes a memory circuit 56 for storing image data is arranged behind a circuit board that includes the drive and processing circuit 55.
A circuit board that includes a wireless communication circuit 57 is arranged behind the circuit board that includes the memory circuit 56. Additionally, two button-type batteries 58, 58 are provided behind the circuit board that includes the wireless communication circuit 57. An antenna 59 that is connected to the wireless communication circuit 57 is provided within the capsule endoscope.
After being swallowed, the capsule endoscope having the structure described above proceeds within the digestive tract of the person undergoing examination while emitting light from the light source 54 in order to illuminate a site in front of the capsule endoscope and to form an image of the illuminated site. An image of such a site, termed herein an ‘observation target site’, is formed on the image pickup surface of the image pickup device 53 by the objective optical system 52. The observation target site image captured by the image pickup device 53 is digitally processed by the drive and processing circuit 55 and the digitally processed image data is stored by the memory circuit 56. The stored image data is then transmitted by the wireless communication circuit 57 via the antenna 59 to an external antenna (not shown in the drawings) and displayed on a display system (not shown in the drawings).
When inserted into the body, a capsule endoscope causes significantly less pain to a patient during in vivo examination as compared with the pain caused by inserting a prior art endoscope having a tubular insertion part.
Recently, it has been noticed that examining the junction between the esophagus and the stomach for “Barrett's esophagus” is important for the early detection of esophageal cancer and/or for the detection of a lesion before it becomes cancerous. “Barrett's esophagus” is a syndrome in which mucosal tissue similar to the gastric mucosa develops in the esophagus after stomach acid refluxes into the esophagus and this process continues over a prolonged period of time. When the tissue of the esophagus has deteriorated to the point of “Barrett's esophagus,” the tissue of the esophagus is very likely to turn cancerous. Therefore, “Barrett's esophagus” is considered to be a pre-cancerous condition.
In order to improve the accuracy of the diagnosis of “Barrett's esophagus,” it is important to observe the tissue around the junction between the esophagus and the stomach, both from the esophagus side and from the stomach side, so that any lesion present will not be overlooked.
The prior art capsule endoscope disclosed in U.S. Pat. No. 6,939,295 provides for observation only in one direction, that is, in the direction of travel through the body. It is not constructed for observation in two opposite directions, forward and backward, along the traveling direction. Therefore, the capsule endoscope disclosed in U.S. Pat. No. 6,939,295 is not capable of a highly accurate diagnosis of “Barrett's esophagus.”
On the other hand, the capsule endoscope described in International Patent Publication WO 02/054932A2 includes illumination systems 61, 61′, objective optical systems 62, 62′, image pickup devices 63, 63′ (such as CCDs) arranged in dome-shaped transparent covers 60, 60′ at both ends of the capsule, respectively, so that observations can be made of images of observation target sites in both the forward and backward directions along the travel path. These structures are arranged in the capsule endoscope, along with batteries 64, 64, an antenna 65, and a transmitter 66.
However, when two image pickup devices are provided as in the capsule endoscope described in International Patent Publication WO 02/054932A2, the following problems occur. First, a significant amount of power is required to drive a solid state image pickup element that forms an image pickup device such as a CCD. When two CCDs are provided, the driving power is doubled, requiring a large battery within the capsule endoscope. Additionally, each CCD requires a drive circuit, inevitably increasing the capsule size in order to provide for a space in which to house the required structures.
In addition, the capsule endoscope passes through the esophagus at a relatively high speed for making observations. In order to minimize the chance of overlooking a lesion, an observation image should be acquired at each observation point in as short a time as possible. In other words, the image pickup device must have a high frame rate. The observation image acquisition time of a capsule endoscope is determined by the time required for the image pickup device to capture an image and the time required for the image to be wirelessly transmitted. Hence, when two image pickup devices are provided in a capsule endoscope, at least the following steps are involved: (1) capturing an image by one of the image pickup devices; (2) transferring the captured image data to the outside of the capsule endoscope by the communication device; (3) capturing an image by the other image pickup device; and (4) transferring the captured image data to the outside of the capsule endoscope by the communication device. Therefore, the observation image acquisition time is doubled in comparison with the prior art observation capsule endoscope described in U.S. Pat. No. 6,939,295 that observes in only one direction. Consequently, the capsule endoscope described in International Patent Publication WO 02/054932A2 proceeds twice the distance within the esophagus before the next observation image in a given viewing direction is captured. Thus, the prior art capsule endoscope having two image pickup devices may fail to prevent “Barrett's esophagus” from being overlooked.